Silicone mixtures with polyurethane have been used since the 1960's to create urological implantable devices. Before that, latex and other rubber type mixtures have been used to mold into urinary catheters or other medical tubing. Besides coatings and proprietary ratios of silicone and polyurethane, there has been very little change in the substance(s) used for these types of catheters. There is a need for alternative silicone compositions that provide anti-microbial resistance. Anti-microbial resistance may refer to the tendency or ability of the silicone to prevent or mitigate encrustation or blockage of a catheter. Further, anti-microbial resistance may refer to the tendency or ability of the silicone to resist having cellular or biological buildup on the device (e.g., anti-biofilm properties). There is a need for such a composition and devices using the same because of the prevalence of nosocomial infections. The U.S. Center for Disease Control has attributed nosocomial infections as a leading cause of deaths after heart disease, cancer, and stroke. Many of these infections are due to indwelling medical devices such as catheters.
While silicone has particular applications for urinary catheters, anti-microbial silicone based materials are needed to prevent infections of medical devices in other applications. For example, medical devices that utilize silicone is include catheters, diaphragms and seals in dialysis equipment, brain surgery-related products, cosmetic and repair parts, heart surgery-related cardiopulmonary bypass pump tubes, chest tubes, membrane artificial lung products, digestive rubber tubing, duodenal tubing, double-lumen intestinal tubing, feeding tubing, gastric decompression tubes, gastric fistula, gastric lavage tubing, enema tubing, abdominal surgery and reproduction related peritoneal dialysis devices, peritoneal drainage tubes and related devices.
Silicone is increasingly become the material of choice for medical devices because of the relatively recent discovery that the plasticizer agent in the most widely used medical material PVC (used for blood bags, drip tubes, dialysis catheters, etc.) can dissolve in the human body, which puts childbearing women, newborns, premature children, dialysis patients and processing intensive care unit patients at potential exposure risk. Non-PVC materials such as silicone do not have this particular problem.
Silicone-based materials have unique advantages over many other materials and have been widely used for medical device applications, but they are not intrinsically anti-microbial. A known solution for imparting anti-microbial properties in silicone is to apply a surface coating of silver to a base silicone material. Silver is known for centuries as having active anti-microbial properties. For example, small silver particles (e.g., nanoparticles) can be coated on the exterior surface of silicone. The coating of silver on the exterior surface of silicone adds additional process steps and thus increases the overall cost of the silicone manufacturing process.
Attempts have been made to incorporate silver particles within the silicone material. Due to the large surface area of silver nanoparticles, the nanoparticles will tend to aggregate to reduce the total surface energy. Thus, most of the nanoparticles dispersed in polymers will concentrate or aggregate in certain regions of the silicone polymer and will not be uniformly distributed therein. Furno et al. has demonstrated that silver nanoparticles can be embedded within silicone by using super critical carbon dioxide to impregnate silicone with silver. See Furno et al., Silver nanoparticles and polymeric medical devices: a new approach to prevention infection?, Journal of Antimicrobial Chemotherapy, 54, 1019-1025 (2004). While some antimicrobial activity was observed in the silicone produced by the process of Furno et al., the silver nanoparticles were quickly washed out of the elastomer. Silicone thus formed in this fashion would not be suitable for medical devices because the anti-microbial effects would quickly be washed away once exposed to bodily tissues.